A little help ?

My mom keeps sending me links for cute maternity clothes but I’ve never bought maternity clothes(this isn’t my first baby). If I do buy maternity clothes what size should I get? Right now I’m 5’4 and 138 pounds, I wear mostly small medium sized leggings and sweatpants, my shirts are typically medium, and my jeans are usually an 8. Having experience with pregnancy I know quite a bit but I’m lost and confused about maternity clothes. I usually just wear my normal clothes while pregnant and size up if I need to. Also this is my last baby so idk if o want to invest in maternity clothes. Can I get an insight on this?